A conventional butterfly valve is a type of flow control device used to manage a flow of fluid through a section of pipe. The typical butterfly valve includes a hollow cylindrical valve body, a flat, circular valve plate, and a rotatable shaft. The valve plate is disposed within the housing at a point intermediate to the length of the cylindrical housing and secured to a lower portion of the rotatable shaft. An upper portion of the rotatable shaft is coupled to an actuator. During operation, movement of the actuator is translated to the valve plate. As the actuator moves, the valve plate is rotatably positioned within the valve body anywhere from perpendicular to parallel to the direction of the flow of fluid through the valve. When the valve plate is perpendicular to the fluid flow direction, the valve is closed and the fluid is restricted from flowing through the valve. In contrast, when the valve plate is parallel to the fluid flow direction, the valve is fully open and the fluid flow through the valve is at its maximum.
Conventional butterfly valves either have a clearance fit between the valve plate and the flow path to avoid wear, which results in high leakage rates, or have contact between the valve plate and the flow path. Since the radial stiffness of both the valve plate and the valve body are high, a butterfly valve with too low a clearance fit may require high actuation forces and risks jamming and/or high wear rates at any contacting points. The high wear rates of the contacting surfaces result in undesirable leakage of the valve in the closed position. To replace a worn valve plate and prevent further leakage, the valve shaft is removed to provide access to the plate. Removing the valve shaft is often an arduous and time consuming task and, therefore, changing a worn plate can be a difficult and lengthy process.
Moreover, standard butterfly valves sometimes require high actuation torque to move the valve plate, especially from a closed position to an open position. Such high actuation torque is due to, for example, high valve closed seating forces, unseating torques to open the valve after the valve was tightly closed, flow induced torque in the direction of closing the valve, and restrictions of the fully open flow path by the valve plate and shaft requiring a larger valve flow path diameter. As a result of requiring high actuation torque, larger and more costly actuators must be employed to open and close the valve.
A standard butterfly valve has the flow passage extending beyond the valve plate in both directions. Hence, the geometry modifications to the valve plate and shaft assembly, in order to reduce flow induced torque, are limited to locations inside the flow passage diameter when the valve is at any position. These modifications provide only minimal reduction of flow induced torque and may reduce the flow area of the fully open valve.
Further, standard butterfly valves require a valve plate and attendant support structure for the valve plate. In many cases the support structure even requires the valve passage way to be enlarged to accommodate the structure within the butterfly valve housing. The enlarged size of the butterfly valve, due to the support structure, is not only a disadvantage in terms of cost, but also present a disadvantage in certain applications where size and weight considerations are of particular interest.
In view of the above, there is a need for a butterfly valve that reduces the actuation forces needed to open and close the valve, and reduce the overall size and weight of the valve. Embodiments of the invention disclosed herein provide such a butterfly valve. These and other advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.